Wireless communication ranging from WiFi to car door locks has become ubiquitous. Emerging technologies such as wireless sensor networks and the internet of things (IoT) are increasing the demand for wireless devices many-fold. In particular, wireless devices with low production costs, small size (i.e., high degree of miniaturization), and reduced power consumption are in high demand. Lowering the power consumption of and developing new power scavenging strategies for wireless devices is particularly important since long battery life is critical to many applications in these networks. In this regard, in order to develop smaller and less costly devices, both the radio and the accompanying central processing unit (CPU), flash memory, random access memory (RAM), and digital interface blocks of the wireless devices may need to shrink. In general, the devices can be miniaturized by following Moore's law and using ever smaller integrated circuit fabrication technologies. However, many radio architectures are not compatible with lower power supply voltages and reduced headroom voltages, with wider device mismatch, and with peculiar device behaviors resulting from small transistor feature sizes. Additionally, the large die area occupied by inductors prevalent in many traditional radio designs do not shrink at all with the minimum feature size of a technology.
Certain wireless transmitter architectures generate a pair of Cartesian baseband signals called in-phase (I) and quadrature-phase (Q) signals. The I and Q signals are nominally orthogonal, and the I and Q signals are combined and up-modulated to RF frequency in the transmitter using a mixer or an image-rejection mixer. The mixers typically require careful design and substantial power to produce accurate signals. The mixer output signals are amplified to full power for transmission using amplifiers. The signal transmission method using I and Q signals is particularly wasteful for low power modulation wireless standards such as IEEE 802.15.4 or Bluetooth which have a constant-amplitude envelope. In these standards, all of the transmission information is encompassed in the phase of the signal. An alternative approach is therefore needed which directly generates the phase without generating and processing an I-Q signal pair at baseband and then up-modulating to RF.
Hence, new circuit and device architectures are needed for providing transmitters and frequency synthesizer that are small and provide highly efficient transmission for use in wireless communication applications.